/*
 * Copyright  1999-2004 The Apache Software Foundation.
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *
 */
package org.apache.xml.security.c14n.helper;

import org.apache.xml.security.utils.Constants;
import org.w3c.dom.Attr;
import java.io.Serializable;
import java.util.Comparator;

/**
 * Compares two attributes based on the C14n specification.
 *
 * <UL>
 * <LI>Namespace nodes have a lesser document order position than attribute 
 *   nodes.
 * <LI> An element's namespace nodes are sorted lexicographically by
 *   local name (the default namespace node, if one exists, has no
 *   local name and is therefore lexicographically least).
 * <LI> An element's attribute nodes are sorted lexicographically with
 *   namespace URI as the primary key and local name as the secondary
 *   key (an empty namespace URI is lexicographically least).
 * </UL>
 *
 * @author Christian Geuer-Pollmann
 */
public class AttrCompare implements Comparator, Serializable {

    private final static long serialVersionUID = -7113259629930576230L;
    private final static int ATTR0_BEFORE_ATTR1 = -1;
    private final static int ATTR1_BEFORE_ATTR0 = 1;
    private final static String XMLNS=Constants.NamespaceSpecNS;

    /**
     * Compares two attributes based on the C14n specification.
     *
     * <UL>
     * <LI>Namespace nodes have a lesser document order position than 
     *   attribute nodes.
     * <LI> An element's namespace nodes are sorted lexicographically by
     *   local name (the default namespace node, if one exists, has no
     *   local name and is therefore lexicographically least).
     * <LI> An element's attribute nodes are sorted lexicographically with
     *   namespace URI as the primary key and local name as the secondary
     *   key (an empty namespace URI is lexicographically least).
     * </UL>
     *
     * @param obj0 casted Attr
     * @param obj1 casted Attr
     * @return returns a negative integer, zero, or a positive integer as 
     *   obj0 is less than, equal to, or greater than obj1
     *
     */
    public int compare(Object obj0, Object obj1) {

        Attr attr0 = (Attr) obj0;
        Attr attr1 = (Attr) obj1;
        String namespaceURI0 = attr0.getNamespaceURI();      
        String namespaceURI1 = attr1.getNamespaceURI();
      
        boolean isNamespaceAttr0 = XMLNS==namespaceURI0;
        boolean isNamespaceAttr1 = XMLNS==namespaceURI1;

        if (isNamespaceAttr0) {
            if (isNamespaceAttr1) {
                // both are namespaces
                String localname0 = attr0.getLocalName();
                String localname1 = attr1.getLocalName();

                if (localname0.equals("xmlns")) {
                    localname0 = "";
                }

                if (localname1.equals("xmlns")) {
                    localname1 = "";
                }

                return localname0.compareTo(localname1);
            }
            // attr0 is a namespace, attr1 is not
            return ATTR0_BEFORE_ATTR1;
        } 

        if (isNamespaceAttr1) {
            // attr1 is a namespace, attr0 is not
            return ATTR1_BEFORE_ATTR0;
        } 

        // none is a namespace
        if (namespaceURI0 == null) {
      	    if (namespaceURI1 == null) {
      		String name0 = attr0.getName();
      		String name1 = attr1.getName();
      		return name0.compareTo(name1);
      	    }
      	    return ATTR0_BEFORE_ATTR1;
        } 

        if (namespaceURI1 == null) {
	    return ATTR1_BEFORE_ATTR0;
        } 

        int a = namespaceURI0.compareTo(namespaceURI1);
        if (a != 0) {
      	    return a;
        }
      
        return (attr0.getLocalName()).compareTo(attr1.getLocalName());
    }
}